This invention relates to a method of operating a vortex or fluidized bed furnace of the kind in which the pulverised fuel, in particular pit coal, is fed into the cooled vortex bed and is burnt there, and in which an agent which absorbs sulphur is placed in the vortex bed.
It is known that fuels which are high in ballast and which contain sulphur and nitrogen can be burnt in a vortex bed at relatively low temperatures (800.degree.-900.degree. C.) to reduce the formation of NO.sub.x and, with the addition of an agent which absorbs sulphur, to reduce the formation of SO.sub.2. The known vortex bed furnaces are large in volume with regard to burning performance in comparison with dust burner furnaces. In addition, the devices required for feeding fuel and the sulphur-absorbing additives into the vortex bed are of complicated construction and susceptible to trouble.
In operating the vortex bed, the fine portion of the pulverised fuel is blown out of the vortex bed by the fluidising and combustion air, without the particles being ignited and burnt. Furthermore, in a vortex bed furnace only a partial load of around 75% of the full load can be achieved without subdividing the bed. When the vortex bed is ignited with hot air, the ignition temperature is gained relatively late, whereby a sudden arcing of the bed can occur. Excess temperatures can thereby occur in the combustion chamber and in the devices connected to this chamber, such as, for example, the bag filter for flue gas separation.
In radiant furnaces or coal dust furnaces, smaller structural volumes can be obtained in relation to burning performance, and the partial load can be reduced to 30% of the full load. However, an extensive combustion which is low in SO.sub.2 is not possible, especially with pit coal, so that the flue gases containing SO.sub.2 produced during combustion are desulphurised after cooling in special flue gas desulphurisation plants. It is therefore attempted to remove at least part of the sulphur from the fuel by mechanical or electrical means by special fuel preparation processes. The problem of the NO.sub.x formation in the dust burners has not yet been satisfactorily solved.
The object of the present invention, therefore, is to produce a method for operating a vortex bed furnace which permits an increase in the relative burning performance and which simplifies the loading of the vortex bed.